This project builds upon our previous research that has been directed toward identifying the origins of micrographia, a handwriting impairment associated with Parkinson's disease, characterized by the progressive diminution of letter size. In this application finger, wrist, and arm movements in handwriting and drawing tasks are investigated by measuring the movements of the pen tip on an electronic display. To get more insight into the involved mechanisms, we use a neural network model of movement production based on anatomical, neurophysiological, pharmacological, and clinical studies. We propose 10 experiments that examine four main hypotheses originating from our recent research that can potentially explain aspects of micrographia. (1) PD patients have problems in coordinating multiple joint movements. This postulates that writing size is reduced when the arm, shoulder and wrist are used, compared to single joint movements. This leads us to predict that PD patients when executing complex movements simplify the coordination by producing a sequence of single joint movements. (2) PD patients have a reduced range of isochronic writing. This predicts that PD patients reduce size when they attempt to produce large movement amplitudes. Furthermore, due to the large inertial forces in arm movements, PD patients are predicted to exhibit a greater speed-size tradeoff for arm compared to fingers and wrist movements. (3) PD patients have increased joint stiffness. This predicts that PD patients will have force saturation problems due to inappropriate muscle activation when making small paced movements or fast normal sized movements with predetermined size. (4) PD patients have reduced sensory feedback. Reduced feedback is predicted to create movement outcome uncertainty which is compensated for by smaller movement sizes. This prediction will be verified by amplifying or degrading feedback. The present series of experiments constitute a comprehensive examination of the origins of reduced movement amplitude in PD.